Step 3:
Heat 2 Tbsp. butter with 1 Tbsp. olive oil in a large skillet. Add chicken & brown lightly on both sides.
Pour Champagne into pan, set lid ajar and simmer until chicken is done and Champagne is reduced to half, about 15 to 20 minutes).

Step 4:
Heat remaining Tbsp. of butter in a small skillet and lightly brown mushrooms

Step 5:
Remove chicken to a warm platter and blot excess liquid. Sprinkle mushrooms on top and keep warm in oven, if desired.